双端队列或双端队列是序列容器,两端都有扩展和收缩函数。它们类似于向量,但是在元素的结尾和开始处插入和删除时效率更高。与向量不同,可能无法保证连续的存储分配。
deque::at()
at()函数用于参考在作为函数参数给出的位置上存在的元素。句法:
dequename.at(position) 参数: Position of the element to be fetched. 返回: Direct reference to the element at the given position.
例子:
Input : mydeque = 1, 2, 3 mydeque.at(2); Output: 3 Input : mydeque = 3, 4, 1, 7, 3 mydeque.at(3); Output: 7
错误和异常
1.如果双端队列中不存在该位置,则抛出out_of_range。 2.否则,它具有强大的无异常抛出保证。
// CPP program to illustrate
// Implementation of at() function
#include <deque>
#include <iostream>
using namespace std;
int main()
{
deque<int> mydeque;
mydeque.push_back(3);
mydeque.push_back(4);
mydeque.push_back(1);
mydeque.push_back(7);
mydeque.push_back(3);
cout << mydeque.at(3);
return 0;
}
输出:
7
应用
给定整数双端队列,请打印出现在偶数位置的所有整数。
Input :1, 2, 3, 4, 5, 6, 7, 8, 9 Output:1 3 5 7 9 Explanation - 1, 3, 5, 7 and 9 are at position 0, 2, 4, 6 and 8 which are even
算法
1.循环运行直至达到阵列大小。
2.检查该位置是否可被2整除,如果是,则在该位置打印元素。
// CPP program to illustrate
// Application of at() function
#include <deque>
#include <iostream>
using namespace std;
int main()
{
deque<int> mydeque;
mydeque.push_back(1);
mydeque.push_back(2);
mydeque.push_back(3);
mydeque.push_back(4);
mydeque.push_back(5);
mydeque.push_back(6);
mydeque.push_back(7);
mydeque.push_back(8);
mydeque.push_back(9);
// Deque becomes 1, 2, 3, 4, 5, 6, 7, 8, 9
for (int i = 0; i < mydeque.size(); ++i) {
if (i % 2 == 0) {
cout << mydeque.at(i);
cout << " ";
}
}
return 0;
}
输出:
1 3 5 7 9
deque::swap()
此函数用于将一个双端队列的内容与相同类型和大小的另一个双端队列交换。
用法:
dequename1.swap(dequename2) 参数: The name of the deque with which the contents have to be swapped. Result: All the elements of the 2 deque are swapped.
例子:
Input :mydeque1 = {1, 2, 3, 4} mydeque2 = {3, 5, 7, 9} mydeque1.swap(mydeque2); Output:mydeque1 = {3, 5, 7, 9} mydeque2 = {1, 2, 3, 4} Input :mydeque1 = {1, 3, 5, 7} mydeque2 = {2, 4, 6, 8} mydeque1.swap(mydeque2); Output:mydeque1 = {2, 4, 6, 8} mydeque2 = {1, 3, 5, 7}
错误和异常
1.如果双端队列的类型不同,则会引发错误。
2.如果双端队列大小不同,则会引发错误。
2.它具有基本的无异常抛出保证。
// CPP program to illustrate
// Implementation of swap() function
#include <deque>
#include <iostream>
using namespace std;
int main()
{
// deque container declaration
deque<int> mydeque1{ 1, 2, 3, 4 };
deque<int> mydeque2{ 3, 5, 7, 9 };
// using swap() function to swap elements of deques
mydeque1.swap(mydeque2);
// printing the first deque
cout << "mydeque1 = ";
for (auto it = mydeque1.begin(); it < mydeque1.end(); ++it)
cout << *it << " ";
// printing the second deque
cout << endl
<< "mydeque2 = ";
for (auto it = mydeque2.begin(); it < mydeque2.end(); ++it)
cout << *it << " ";
return 0;
}
输出:
mydeque1 = 3 5 7 9 mydeque2 = 1 2 3 4
相关用法
注:本文由纯净天空筛选整理自AyushSaxena大神的英文原创作品 deque::at() and deque::swap() in C++ STL。非经特殊声明,原始代码版权归原作者所有,本译文未经允许或授权,请勿转载或复制。